Conductive thermosets by extrusion

ABSTRACT

Methods of preparing conductive thermoset precursors containing carbon nanotubes is provided. Also provided is a method of preparing conductive thermosets containing carbon nanotubes. The carbon nanotubes may in individual form or in the form of aggregates having a macromorpology resembling the shape of a cotton candy, bird nest, combed yarn or open net. Preferred multiwalled carbon nanotubes have diameters no greater than 1 micron and preferred single walled carbon nanotubes have diameters less than 5 nm. Carbon nanotubes may be adequately dispersed in a thermoset precursor by using a extrusion process generally reserved for thermoplastics. The thermoset precursor may be a precursor for epoxy, phenolic, polyimide, urethane, polyester, vinyl ester or silicone. A preferred thermoset precursor is a bisphenol A derivative.

CROSS REFERENCE INFORMATION

This is a continuation of U.S. Ser. No. 11/218,209, filed Aug. 31, 2005,issued as U.S. Pat. No. 7,566,749, which claims priority and the benefitof U.S. Provisional Application No. 60/605,769, filed Aug. 31, 2004, allof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates broadly to conductive thermosets and conductivethermoset precursors containing carbon nanotubes. The conductivethermoset precursors are prepared by extrusion and are used to preparethe conductive thermosets.

2. Description of the Related Art

Conductive Polymers

Conductive polymers have long been in demand and offer a number ofbenefits for a variety of applications due to their combined polymericand conductive properties. The polymeric ingredient in conductivepolymers can take the form of thermoplastics or thermosets. Generalbackground information on these polymers may be found in numerouspublications such as International Plastics Handbook, translated by JohnHaim and David Hyatt, 3^(rd) edition, Hanser/Gardner Publications (1995)and Mixing and Compounding of Polymers—Theory and Practice, edited byIca Manas-Zloczower and Zehev Tadmor, Hanser/Gardner Publications(1994), both of which are hereby incorporated by reference. Theconductive element of the conductive polymer includes metallic powder orcarbon black.

Thermoplastics, by their malleable and flexible nature, have proven tobe more commercially practical and viable when forming conductivepolymers. E.g., U.S. Pat. No. 5,591,382, filed Mar. 30, 1994 to Nahass,et al., hereby incorporated by reference. Thermoplastics are easy to mixwith conductive additives by an extrusion process to form a conductivethermoplastic polymer. Furthermore, thermoplastics can be softened uponheating so as to reshape the thermoplastic as necessary. However,thermoplastics lack the strength of thermosets, which crosslink to formstronger polymers. Recent technological developments permit the additionof crosslinking agents to thermoplastics to endow the thermoplastic withgreater strength, although such process has its own disadvantages aswell (e.g., extra cost, effort, experimentation, etc.)

On the other hand, thermosets, which are more rigid and inflexible innature, are difficult to mix with conductive additives to form aconductive thermoset polymer. Unlike thermoplastics, thermoset polymersare typically formed through a chemical reaction with at least twoseparate components or precursors. The chemical reaction may include useof catalysts, chemicals, energy, heat, or radiation so as to fosterintermolecular bonding such as crosslinking. Different thermosets can beformed with different reactions to foster intermolecular bonding. Thethermoset bonding/forming process is often referred to as curing. Thethermoset components or precursors are usually liquid or malleable priorto curing, and are designed to be molded into their final form, or usedas adhesive. Once cured, however, a thermoset polymer is stronger thanthermoplastic and is also better suited for high temperatureapplications since it cannot be easily softened, remelted, or remoldedon heating like thermoplastics. Thus, conductive thermoset polymersoffer the industry a much desired combination of strength andconductivity.

Unlike thermoplastics which can be melted so as to add and disperseconductive additives via extrusion, thermosets cannot be melted once thethermoset has been cured. Rather, conductive additives must be added anddispersed into the precursor components before the final cured thermosetproduct is formed. This requirement creates a number of limitations informing conductive thermosets. For example, extrusion, which is apreferred and efficient method for dispersing additives inthermoplastics, is generally not used with thermoset precursors sincethey typically do not have sufficient viscosity to permit the successfuldispersion of the conductive additives in the precursors.

Rather, sonication, stirring or milling are the preferred methods todisperse conductive additives in thermosets. However, these methods aredifficult to scale up for commercial uses, and have not yieldedconsistent and practical results in forming conductive thermosetpolymers. For example, when forming conductive thermoset, typically aconductive additive is mixed into a first liquid precursor and stirredtherein. However, adding a conductive additive increases the viscosityof the first liquid precursor and thus increases the difficulty inmixing. Therefore, there is an inherent limit as to how much conductiveadditive can be practically added to the first liquid precursor. Themixed first liquid precursor is then added to and reacted with a secondliquid precursor of lower viscosity (if the second liquid precursor wasof higher viscosity, mixing would be even more difficult) to form thethermoset polymer or resin. However, by mixing the first mixed precursorwith the second liquid precursor, the total conductive additive loadingis further decreased with respect to the final thermoset product,usually rendering the final conductive thermoset product commerciallynonviable.

As such, there is a need for a new method for forming conductivethermosets.

Carbon Nanotubes

There are a number of known conductive additives in the art, includingcarbon black, carbon fibers, carbon fibrils, metallic powder, etc.Carbon fibrils have grown in popularity due to its extremely highconductivity and strength compared to other conductive additives.

Carbon fibrils are commonly referred to as carbon nanotubes. Carbonfibrils are vermicular carbon deposits having diameters less than 1.0μ,preferably less than 0.5μ, and even more preferably less than 0.2μ. Theyexist in a variety of forms and have been prepared through the catalyticdecomposition of various carbon-containing gases at metal surfaces. Suchvermicular carbon deposits have been observed almost since the advent ofelectron microscopy. (Baker and Harris, Chemistry and Physics of Carbon,Walker and Thrower ed., Vol. 14, 1978, p. 83; Rodriguez, N., J. Mater.Research, Vol. 8, p. 3233 (1993)).

In 1976, Endo et al. (see Obelin, A. and Endo, M., J. of Crystal Growth,Vol. 32 (1976), pp. 335-349), hereby incorporated by reference,elucidated the basic mechanism by which such carbon fibrils grow. Theywere seen to originate from a metal catalyst particle, which, in thepresence of a hydrocarbon containing gas, becomes supersaturated incarbon. A cylindrical ordered graphitic core is extruded whichimmediately, according to Endo et al., becomes coated with an outerlayer of pyrolytically deposited graphite. These fibrils with apyrolytic overcoat typically have diameters in excess of 0.1μ, moretypically 0.2 to 0.5μ.

In 1983, Tennent, U.S. Pat. No. 4,663,230, hereby incorporated byreference, describes carbon fibrils that are free of a continuousthermal carbon overcoat and have multiple graphitic outer layers thatare substantially parallel to the fibril axis. As such they may becharacterized as having their c-axes, the axes which are perpendicularto the tangents of the curved layers of graphite, substantiallyperpendicular to their cylindrical axes. They generally have diametersno greater than 0.1μ and length to diameter ratios of at least 5.Desirably they are substantially free of a continuous thermal carbonovercoat, i.e., pyrolytically deposited carbon resulting from thermalcracking of the gas feed used to prepare them. Thus, the Tennentinvention provided access to smaller diameter fibrils, typically 35 to700 Å (0.0035 to 0.070μ) and to an ordered, “as grown” graphiticsurface. Fibrillar carbons of less perfect structure, but also without apyrolytic carbon outer layer have also been grown.

The carbon nanotubes which can be oxidized as taught in thisapplication, are distinguishable from commercially available continuouscarbon fibers. In contrast to these fibers which have aspect ratios(L/D) of at least 10⁴ and often 10⁶ or more, carbon fibrils havedesirably large, but unavoidably finite, aspect ratios. The diameter ofcontinuous fibers is also far larger than that of fibrils, beingalways >1.0μ and typically 5 to 7μ.

Tennent, et al., U.S. Pat. No. 5,171,560, hereby incorporated byreference, describes carbon fibrils free of thermal overcoat and havinggraphitic layers substantially parallel to the fibril axes such that theprojection of said layers on said fibril axes extends for a distance ofat least two fibril diameters. Typically, such fibrils are substantiallycylindrical, graphitic nanotubes of substantially constant diameter andcomprise cylindrical graphitic sheets whose c-axes are substantiallyperpendicular to their cylindrical axis. They are substantially free ofpyrolytically deposited carbon, have a diameter less than 0.1μ andlength to diameter ratio of greater than 5. These fibrils can beoxidized by the methods of the invention.

When the projection of the graphitic layers on the nanotube axis extendsfor a distance of less than two nanotube diameters, the carbon planes ofthe graphitic nanotube, in cross section, take on a herring boneappearance. These are termed fishbone fibrils. Geus, U.S. Pat. No.4,855,091, hereby incorporated by reference, provides a procedure forpreparation of fishbone fibrils substantially free of a pyrolyticovercoat. These carbon nanotubes are also useful in the practice of theinvention.

Carbon nanotubes of a morphology similar to the catalytically grownfibrils described above have been grown in a high temperature carbon arc(Iijima, Nature 354, 56, 1991). It is now generally accepted (Weaver,Science 265, 1994) that these arc-grown nanofibers have the samemorphology as the earlier catalytically grown fibrils of Tennent. Arcgrown carbon nanofibers after colloquially referred to as “bucky tubes”,are also useful in the invention.

Useful single walled carbon nanotubes and process for making them aredisclosed, for example, in “Single-shell carbon nanotubes of 1-nmdiameter”, S Iijima and T Ichihashi Nature, vol. 363, p. 603 (1993) and“Cobalt-catalysed growth of carbon nanotubes with single-atomic-layerwalls,” D S Bethune, C H Kiang, M S DeVries, G Gorman, R Savoy and RBeyers Nature, vol. 363, p. 605 (1993), both articles of which arehereby incorporated by reference.

Single walled carbon nanotubes are also disclosed in U.S. Pat. No.6,221,330 to Moy et. al., hereby incorporated by reference. Moydisclosed a process for producing hollow, single-walled carbon nanotubesby catalytic decomposition of one or more gaseous carbon compounds byfirst forming a gas phase mixture carbon feed stock gas comprising oneor more gaseous carbon compounds, each having one to six carbon atomsand only H, O, N, S or Cl as hetero atoms, optionally admixed withhydrogen, and a gas phase metal containing compound which is unstableunder reaction conditions for said decomposition, and which forms ametal containing catalyst which acts as a decomposition catalyst underreaction conditions; and then conducting said decomposition reactionunder decomposition reaction conditions, thereby producing saidnanotubes. The invention relates to a gas phase reaction in which a gasphase metal containing compound is introduced into a reaction mixturealso containing a gaseous carbon source. The carbon source is typicallya C₁ through C₆ compound having as hetero atoms H, O, N, S or Cl,optionally mixed with hydrogen. Carbon monoxide or carbon monoxide andhydrogen is a preferred carbon feedstock. Increased reaction zonetemperatures of approximately 400° C. to 1300° C. and pressures ofbetween about 0 and about 100 p.s.i.g., are believed to causedecomposition of the gas phase metal containing compound to a metalcontaining catalyst. Decomposition may be to the atomic metal or to apartially decomposed intermediate species. The metal containingcatalysts (1) catalyze CO decomposition and (2) catalyze SWNT formation.Thus, the invention also relates to forming SWNT via catalyticdecomposition of a carbon compound.

The invention of U.S. Pat. No. 6,221,330 may in some embodiments employan aerosol technique in which aerosols of metal containing catalysts areintroduced into the reaction mixture. An advantage of an aerosol methodfor producing SWNT is that it will be possible to produce catalystparticles of uniform size and scale such a method for efficient andcontinuous commercial or industrial production. The previously discussedelectric arc discharge and laser deposition methods cannot economicallybe scaled up for such commercial or industrial production. Examples ofmetal containing compounds useful in the invention include metalcarbonyls, metal acetyl acetonates, and other materials which underdecomposition conditions can be introduced as a vapor which decomposesto form an unsupported metal catalyst. Catalytically active metalsinclude Fe, Co, Mn, Ni and Mo. Molybdenum carbonyls and iron carbonylsare the preferred metal containing compounds which can be decomposedunder reaction conditions to form vapor phase catalyst. Solid forms ofthese metal carbonyls may be delivered to a pretreatment zone where theyare vaporized, thereby becoming the vapor phase precursor of thecatalyst. It was found that two methods may be employed to form SWNT onunsupported catalysts.

The first method is the direct injection of volatile catalyst. Thedirect injection method is described is U.S. application Ser. No.08/459,534, incorporated herein by reference. Direct injection ofvolatile catalyst precursors has been found to result in the formationof SWNT using molybdenum hexacarbonyl [Mo(CO)₆] and dicobaltoctacarbonyl [CO₂ (CO)₈] catalysts. Both materials are solids at roomtemperature, but sublime at ambient or near-ambient temperatures—themolybdenum compound is thermally stable to at least 150°, the cobaltcompound sublimes with decomposition “Organic Syntheses via MetalCarbonyls,” Vol. 1, I. Wender and P. Pino, eds., IntersciencePublishers, New York, 1968, p. 40).

The second method uses a vaporizer to introduce the metal containingcompound (FIG. 12). In one preferred embodiment of the invention, thevaporizer 10, shown at FIG. 12, comprises a quartz thermowell 20 havinga seal 24 about 1″ from its bottom to form a second compartment. Thiscompartment has two ¼″ holes 26 which are open and exposed to thereactant gases. The catalyst is placed into this compartment, and thenvaporized at any desired temperature using a vaporizer furnace 32. Thisfurnace is controlled using a first thermocouple 22. A metal containingcompound, preferably a metal carbonyl, is vaporized at a temperaturebelow its decomposition point, reactant gases CO or CO/H₂ sweep theprecursor into the reaction zone 34, which is controlled separately by areaction zone furnace 38 and second thermocouple 42. Although applicantsdo not wish to be limited to a particular theory of operability, it isbelieved that at the reactor temperature, the metal containing compoundis decomposed either partially to an intermediate species or completelyto metal atoms. These intermediate species and/or metal atoms coalesceto larger aggregate particles which are the actual catalyst. Theparticle then grows to the correct size to both catalyze thedecomposition of CO and promote SWNT growth. In the apparatus of FIG.11, the catalyst particles and the resultant carbon forms are collectedon the quartz wool plug 36. Rate of growth of the particles depends onthe concentration of the gas phase metal containing intermediatespecies. This concentration is determined by the vapor pressure (andtherefore the temperature) in the vaporizer. If the concentration is toohigh, particle growth is too rapid, and structures other than SWNT aregrown (e.g., MWNT, amorphous carbon, onions, etc.) All of the contentsof U.S. Pat. No. 6,221,330, including the Examples described therein,are hereby incorporated by reference.

U.S. Pat. No. 5,424,054 to Bethune et al., hereby incorporated byreference, describes a process for producing single-walled carbonnanotubes by contacting carbon vapor with cobalt catalyst. The carbonvapor is produced by electric arc heating of solid carbon, which can beamorphous carbon, graphite, activated or decolorizing carbon or mixturesthereof. Other techniques of carbon heating are discussed, for instancelaser heating, electron beam heating and RF induction heating.

Smalley (Guo, T., Nikoleev, P., Thess, A., Colbert, D. T., and Smalley,R. E., Chem. Phys. Lett. 243: 1-12 (1995)), hereby incorporated byreference, describes a method of producing single-walled carbonnanotubes wherein graphite rods and a transition metal aresimultaneously vaporized by a high-temperature laser.

Smalley (Thess, A., Lee, R., Nikolaev, P., Dai, H., Petit, P., Robert,J., Xu, C., Lee, Y. H., Kim, S. G., Rinzler, A. G., Colbert, D. T.,Scuseria, G. E., Tonarek, D., Fischer, J. E., and Smalley, R. E.,Science, 273: 483-487 (1996)), hereby incorporated by reference, alsodescribes a process for production of single-walled carbon nanotubes inwhich a graphite rod containing a small amount of transition metal islaser vaporized in an oven at about 1200° C. Single-wall nanotubes werereported to be produced in yields of more than 70%.

Supported metal catalysts for formation of SWNT are also known. Smalley(Dai., H., Rinzler, A. G., Nikolaev, P., Thess, A., Colbert, D. T., andSmalley, R. E., Chem. Phys. Lett. 260: 471-475 (1996)), herebyincorporated by reference, describes supported Co, Ni and Mo catalystsfor growth of both multiwalled nanotubes and single-walled nanotubesfrom CO, and a proposed mechanism for their formation.

Carbon nanotubes differ physically and chemically from continuous carbonfibers which are commercially available as reinforcement materials, andfrom other forms of carbon such as standard graphite and carbon black.Standard graphite, because of its structure, can undergo oxidation toalmost complete saturation. Moreover, carbon black is amorphous carbongenerally in the form of spheroidal particles having a graphenestructure, carbon layers around a disordered nucleus. The differencesmake graphite and carbon black poor predictors of nanotube chemistry.

Aggregates of Carbon Nanotubes

As produced, carbon nanotubes may be in the form of discrete nanotubes,aggregates of nanotubes or both.

Nanotubes produced or prepared as aggregates have various morphologies(as determined by scanning electron microscopy) in which they arerandomly entangled with each other to form entangled balls of nanotubesresembling bird nests (“BN”); or as aggregates consisting of bundles ofstraight to slightly bent or kinked carbon nanotubes havingsubstantially the same relative orientation, and having the appearanceof combed yarn (“CY”) e.g., the longitudinal axis of each nanotube(despite individual bends or kinks) extends in the same direction asthat of the surrounding nanotubes in the bundles; or, as, aggregatesconsisting of straight to slightly bent or kinked nanotubes which areloosely entangled with each other to form an “open net” (“ON”)structure. In open net structures the extent of nanotube entanglement isgreater than observed in the combed yarn aggregates (in which theindividual nanotubes have substantially the same relative orientation)but less than that of bird nest. Other useful aggregate structuresinclude the cotton candy (“CC”) structure, which is similar to the CYstructure.

The morphology of the aggregate is controlled by the choice of catalystsupport. Spherical supports grow nanotubes in all directions leading tothe formation of bird nest aggregates. Combed yarn and open netaggregates are prepared using supports having one or more readilycleavable planar surfaces, e.g., an iron or iron-containing metalcatalyst particle deposited on a support material having one or morereadily cleavable surfaces and a surface area of at least 1 squaremeters per gram. Moy et al., U.S. application Ser. No. 08/469,430entitled “Improved Methods and Catalysts for the Manufacture of CarbonFibrils”, filed Jun. 6, 1995, hereby incorporated by reference,describes nanotubes prepared as aggregates having various morphologies(as determined by scanning electron microscopy).

Further details regarding the formation of carbon nanotube or nanofiberaggregates may be found in the disclosure of U.S. Pat. No. 5,165,909 toTennent; U.S. Pat. No. 5,456,897 to Moy et al.; Snyder et al., U.S.patent application Ser. No. 07/149,573, filed Jan. 28, 1988, and PCTApplication No. US89/00322, filed Jan. 28, 1989 (“Carbon Fibrils”) WO89/07163, and Moy et al., U.S. patent application Ser. No. 413,837 filedSep. 28, 1989 and PCT Application No. US90/05498, filed Sep. 27, 1990(“Battery”) WO 91/05089, and U.S. application Ser. No. 08/479,864 toMandeville et al., filed Jun. 7, 1995 and U.S. application Ser. No.08/284,917, filed Aug. 2, 1994 and U.S. application Ser. No. 08/320,564,filed Oct. 11, 1994 by Moy et al., all of which are assigned to the sameassignee as the invention here and are hereby incorporated by reference.

Oxidation and/or Functionalization of Carbon Nanotubes

Carbon nanotubes or aggregates may be oxidized to enhance certaindesirable properties. For example, oxidation can be used to add certaingroups onto the surface of the carbon nanotubes or carbon nanotubeaggregates, to loosen the entanglement of the carbon nanotubeaggregates, to reduce the mass or remove the end caps off the carbonnanotubes, etc.

McCarthy et al., U.S. patent application Ser. No. 08/329,774 filed Oct.27, 1994, hereby incorporated by reference, describes processes foroxidizing the surface of carbon fibrils that include contacting thefibrils with an oxidizing agent that includes sulfuric acid (H₂SO₄) andpotassium chlorate (KClO₃) under reaction conditions (e.g., time,temperature, and pressure) sufficient to oxidize the surface of thefibril. The fibrils oxidized according to the processes of McCarthy, etal. are non-uniformly oxidized, that is, the carbon atoms aresubstituted with a mixture of carboxyl, aldehyde, ketone, phenolic andother carbonyl groups.

Fibrils have also been oxidized non-uniformly by treatment with nitricacid. International Application PCT/US94/10168 filed on Sep. 9, 1994 asWO95/07316 discloses the formation of oxidized fibrils containing amixture of functional groups. Hoogenvaad, M. S., et al. (“MetalCatalysts supported on a Novel Carbon Support,” presented at SixthInternational Conference on Scientific Basis for the Preparation ofHeterogeneous Catalysts, Brussels, Belgium, September 1994) also foundit beneficial in the preparation of fibril-supported precious metals tofirst oxidize the fibril surface with nitric acid. Such pretreatmentwith acid is a standard step in the preparation of carbon-supportednoble metal catalysts, where, given the usual sources of such carbon, itserves as much to clean the surface of undesirable materials as tofunctionalize it.

In published work, McCarthy and Bening (Polymer Preprints ACS Div. ofPolymer Chem. 30 (1)420 (1990)) prepared derivatives of oxidized fibrilsin order to demonstrate that the surface comprised a variety of oxidizedgroups. The compounds they prepared, phenylhydrazones,haloaromaticesters, thallous salts, etc., were selected because of theiranalytical utility, being, for example, brightly colored, or exhibitingsome other strong and easily identified and differentiated signal. Thesecompounds were not isolated and are, unlike the derivatives describedherein, of no practical significance.

Fischer et al., U.S. Ser. No. 08/352,400 filed Dec. 8, 1994, Fischer etal., U.S. Ser. No. 08/812,856 filed Mar. 6, 1997, Tennent et al., U.S.Ser. No. 08/856,657 filed May 15, 1997, Tennent, et al., U.S. Ser. No.08/854,918 filed May 13, 1997, and Tennent et al., U.S. Ser. No.08/857,383 filed May 15, 1997, all hereby incorporated by referencedescribe processes for oxidizing the surface of carbon fibrils thatinclude contacting the fibrils with a strong oxidizing agent such as asolution of alkali metal chlorate in a strong acid such as sulfuricacid. Additional useful oxidation treatments for carbon nanotubesinclude those described in Niu, US Published Application No.2005/0002850A1, filed May 28, 2004, hereby incorporated by reference.

Additionally, these applications also describe methods of uniformlyfunctionalizing carbon fibrils by sulfonation, electrophilic addition todeoxygenated fibril surfaces or metallation. Sulfonation of the fibrilscan be accomplished with sulfuric acid or SO₃ in vapor phase which givesrise to carbon fibrils bearing appreciable amounts of sulfones so muchso that the sulfone functionalized fibrils show a significant weightgain.

U.S. Pat. No. 5,346,683 to Green, et al. describes uncapped and thinnedcarbon nanotubes produced by reaction with a flowing reactant gascapable of reacting selectively with carbon atoms in the capped endregion of arc grown nanotubes.

U.S. Pat. No. 5,641,466 to Ebbesen, et al. describes a procedure forpurifying a mixture of arc grown carbon nanotubes and impurity carbonmaterials such as carbon nanoparticles and possibly amorphous carbon byheating the mixture in the presence of an oxidizing agent at atemperature in the range of 600° C. to 1000° C. until the impuritycarbon materials are oxidized and dissipated into gas phase.

In a published article Ajayan and Tijima (Nature 361, p. 334-337 (1993))discuss annealing of carbon nanotubes by heating them with oxygen in thepresence of lead which results in opening of the capped tube ends andsubsequent filling of the tubes with molten material through capillaryaction.

In other published work, Haddon and his associates ((Science, 282, 95(1998) and J. Mater. Res., Vol. 13, No. 9, 2423 (1998)) describetreating single-walled carbon nanotube materials (SWNTM) withdichlorocarbene and Birch reduction conditions in order to incorporatechemical functionalities into SWNTM. Derivatization of SWNT with thionylchloride and octadecylamine rendered the SWNT soluble in common organicsolvents such as chloroform, dichlororomethane, aromatic solvents andCS₂.

Additionally functionalized nanotubes have been generally discussed inU.S. Ser. No. 08/352,400 filed on Dec. 8, 1994 and in U.S. Ser. No.08/856,657 filed May 15, 1997, both incorporated herein by reference. Inthese applications the nanotube surfaces are first oxidized by reactionwith strong oxidizing or other environmentally unfriendly chemicalagents. The nanotube surfaces may be further modified by reaction withother functional groups. The nanotube surfaces have been modified with aspectrum of functional groups so that the nanotubes could be chemicallyreacted or physically bonded to chemical groups in a variety ofsubstrates.

Complex structures of nanotubes have been obtained by linking functionalgroups on the tubes with one another by a range of linker chemistries.

Representative functionalized nanotubes broadly have the formula[C_(n)H_(L)

R_(m)

where n is an integer, L is a number less than 0. In, m is a number lessthan 0.5 n,

each of R is the same and is selected from SO₃H, COOH, NH₂, OH, O, CHO,CN, COC1, halide, COSH, SH, R′, COOR′, SR′, SiR′₃, Si

OR′

_(y)R′_(3-y), Si

O—SiR′₂

OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X,

y is an integer equal to or less than 3,

R′ is alkyl, aryl, heteroaryl, cycloalkyl aralkyl or heteroaralkyl,

R″ is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl orcycloaryl,

X is halide, and

Z is carboxylate or trifluoroacetate.

The carbon atoms, C_(n), are surface carbons of the nanofiber.

Secondary Derivatives of Oxidized Nanotubes

Oxidized carbon nanotubes or carbon nanotube aggregates can be furthertreated to add secondary functional groups to the surface. In oneembodiment, oxidized nanotubes are further treated in a secondarytreatment step by further contacting with a reactant suitable to reactwith moieties of the oxidized nanotubes thereby adding at least anothersecondary functional group. Secondary derivatives of the oxidizednanotubes are essentially limitless. For example, oxidized nanotubesbearing acidic groups like —COOH are convertible by conventional organicreactions to virtually any desired secondary group, thereby providing awide range of surface hydrophilicity or hydrophobicity.

The secondary group that can be added by reacting with the moieties ofthe oxidized nanotubes include but are not limited to alkyl/aralkylgroups having from 1 to 18 carbons, a hydroxyl group having from 1 to 18carbons, an amine group having from 1 to 18 carbons, alkyl aryl silaneshaving from 1 to 18 carbons and fluorocarbons having from 1 to 18carbons.

SUMMARY OF THE INVENTION

The present invention, which addresses the needs of the prior artprovides a method of preparing conductive thermoset precursorscontaining carbon nanotubes. Also provided is a method of preparingconductive thermosets containing carbon nanotubes.

The carbon nanotubes may be in individual form or in the form ofaggregates having a macromorphology resembling the shape of a cottoncandy, bird nest, combed yarn or open net. Preferred multiwalled carbonnanotubes have diameters no greater than 1 micron and preferred singlewalled carbon nanotubes have diameters less than 5 nm.

It has been discovered that carbon nanotubes may be adequately dispersedin a thermoset precursor by using an extrusion process generallyreserved for thermoplastics. In a preferred embodiment, carbon nanotubesare dispersed by extrusion within a thermoset precursor having aviscosity greater than 15 poise. The thermoset precursor may have aviscosity in the range of 20 to 600 poise or between 50 to 500 poise.The thermoset precursor may be a precursor for epoxy, phenolic,urethane, silicone, polyimide, polyester or vinyl ester. A preferredthermoset precursor is a bisphenol A derivative.

The conductive thermoset precursor preferably contains 0.5 to 30% carbonnanotube or carbon nanotube aggregates by weight.

Where the thermoset precursor contains epoxide, the epoxide weight perequivalent is greater than 600 gram precursor/gram equivalent epoxide,preferably 600 to 4000 gram precursor/gram equivalent epoxide, morepreferably 1000 to 3800 gram precursor/gram equivalent epoxide.

The thermoset precursor may further contain a diluting or let down agentwhich is added to keep the precursor in a viscous non-solid, gel-like orliquid state before mixing with the second thermoset precursor to form aconductive thermoset. Mixers which generate shear, such as Brabendermixer, planetary mixer, multi-shaft mixer, etc. may be used to includeor mix the diluting agent into the conductive thermoset precursor. In apreferred embodiment, the diluting agent is another thermoset precursorwhich does not react upon addition with the first thermoset precursor tocure into or become the final thermoset product.

The melting point of the thermoset precursor may be greater than 30° C.,or conveniently between 30 and 350° C.

Extrusion may be accomplished with a single screw, twin screw or anyother conventional extruders useful for dispersing additives in thethermoset precursor. Furthermore, the twin screw extruder may be counterrotating or co-rotating.

The conductive thermoset precursor prepared according to the presentinvention is then reacted with at least a second thermoset precursor toform a conductive thermoset. The conductive thermoset may have aresistivity less than 10¹¹ ohm-cm, preferably less than 10⁸ ohm-cm, morepreferably less than 10⁶ ohm-cm.

Other improvements which the present invention provides over the priorart will be identified as a result of the following description whichsets forth a preferred embodiments of the present invention. Thedescription is not in any way intended to limit the scope of the presentinvention, but rather only to provide a working example of the presentpreferred embodiments. The scope of the present invention will bepointed out in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The terms “nanotube”, “nanofiber” and “fibril” are used interchangeablyto refer to single walled or multiwalled carbon nanotubes. Each refersto an elongated hollow structure preferably having a cross section(e.g., angular fibers having edges) or a diameter (e.g., rounded) lessthan 1 micron (for multiwalled nanotubes) or less than 5 nm (for singlewalled nanotubes). The term “nanotube” also includes “buckytubes” andfishbone fibrils.

“Multiwalled nanotubes” as used herein refers to carbon nanotubes whichare substantially cylindrical, graphitic nanotubes of substantiallyconstant diameter and comprise a single cylindrical graphitic sheet orlayer whose c-axis is substantially perpendicular to the cylindricalaxis, such as those described, e.g., in U.S. Pat. No. 5,171,560 toTennent, et al. The term “multiwalled nanotubes” is meant to beinterchangeable with all variations of said term, including but notlimited to “multi-wall nanotubes”, “multi-walled nanotubes”, “multiwallnanotubes,” etc.

“Single walled nanotubes” as used herein refers to carbon nanotubeswhich are substantially cylindrical, graphitic nanotubes ofsubstantially constant diameter and comprise cylindrical graphiticsheets or layers whose c-axes are substantially perpendicular to theircylindrical axis, such as those described, e.g., in U.S. Pat. No.6,221,330 to Moy, et al. The term “single walled nanotubes” is meant tobe interchangeable with all variations of said term, including but notlimited to “single-wall nanotubes”, “single-walled nanotubes”, “singlewall nanotubes,” etc.

The term “functional group” refers to groups of atoms that give thecompound or substance to which they are linked characteristic chemicaland physical properties.

A “functionalized” surface refers to a carbon surface on which chemicalgroups are adsorbed or chemically attached.

“Graphenic” carbon is a form of carbon whose carbon atoms are eachlinked to three other carbon atoms in an essentially planar layerforming hexagonal fused rings. The layers are platelets only a few ringsin diameter or they may be ribbons, many rings long but only a few ringswide.

“Graphenic analogue” refers to a structure which is incorporated in agraphenic surface.

“Graphitic” carbon consists of graphenic layers which are essentiallyparallel to one another and no more than 3.6 angstroms apart.

The term “aggregate” refers to a dense, microscopic particulatestructure comprising entangled carbon nanotubes.

The term “precursor” means any component or ingredient which is used inpreparing the final crosslinked or cured polymer product. Precursorsinclude monomers or polymers which have not yet been crosslinked orcured to form the final crosslinked or cured polymer product.

“Thermoplastics” refer generally to a class of polymers that typicallysoften or melt upon heating.

“Thermosets” refer generally to a class of polymers that do not meltupon heating.

The term “viscosity” measures or characterizes the internal resistanceto flow exhibited by a material in a fluid like state. Where a materialsuch as a solid needs to be melted in order to permit flow (e.g.,because solids cannot flow, they have infinite viscosity), the term“melt viscosity” is often used to measure or characterize the internalresistance of the melted material. Therefore, for purposes of thisapplication and terms used herein, the terms “viscosity” and “meltviscosity” are interchangeable since they both measure or characterizethe material or melted material's internal resistance to flow.

Carbon Nanotubes and Carbon Nanotube Aggregates

Any of the carbon nanotubes and carbon nanotube aggregates described inthe Description Of The Related Art under the heading “Carbon Nanotubes”or “Aggregates Of Carbon Nanotubes” may be used in practicing theinvention, and all of those references therein are hereby incorporatedby reference.

The carbon nanotubes preferably have diameters no greater than onemicron, more preferably no greater than 0.2 micron. Even more preferredare carbon nanotubes having diameters between 2 and 100 nanometers,inclusive. Most preferred are carbon nanotubes having diameters lessthan 5 nanometers or between 3.5 and 75 nanometers, inclusive.

The nanotubes are substantially cylindrical, graphitic carbon fibrils ofsubstantially constant diameter and are substantially free ofpyrolytically deposited carbon. The nanotubes include those having alength to diameter ratio of greater than 5 with the projection of thegraphite layers on the nanotubes extending for a distance of at leasttwo nanotube diameters.

Most preferred multiwalled nanotubes are described in U.S. Pat. No.5,171,560 to Tennent, et al., incorporated herein by reference. Mostpreferred single walled nanotubes are described in U.S. Pat. No.6,221,330 to Moy, et al., incorporated herein by reference. Carbonnanotubes prepared according to U.S. Pat. No. 6,696,387 are alsopreferred and incorporated by reference.

The aggregates of carbon nanotubes, which are dense, microscopicparticulate structure comprising entangled carbon nanotubes and whichhave a macromorphology that resembles a birds nest, cotton candy, combedyarn, or open net. As disclosed in U.S. Pat. No. 5,110,693 andreferences therein (all of which are herein incorporated by reference),two or more individual carbon fibrils may form microscopic aggregates ofentangled fibrils. The cotton candy aggregate resembles a spindle or rodof entangled fibers with a diameter that may range from 5 nm to 20 nmwith a length that may range from 0.1 μm to 1000 μm. The birds nestaggregate of fibrils can be roughly spherical with a diameter that mayrange from 0.1 μm to 1000 μm. Larger aggregates of each type (CC and/orBN) or mixtures of each can be formed.

The aggregates of carbon nanotubes may be tightly entangled or may beloosely entangled. If desired, the carbon nanotube aggregates may betreated with an oxidizing agent to further loosen the entanglement ofthe carbon nanotubes without destroying the aggregate structure itself.

Methods of Preparing Conductive Thermoset Precursors and ConductiveThermoset

Preferred thermosets which are useful in forming conductive thermosetsinclude phenolics, ureas, melamines, epoxies, polyesters, vinyl esters,silicones, polyimides, urethanes, and polyurethanes.

As discussed under the earlier heading “Conductive Polymers,” thermosetsare generally formed by chemically reacting at least two separatecomponents or precursors. The chemical reaction may include the use ofcatalysts, chemicals, energy, heat or radiation so as to fosterintermediate bonding such as crosslinking. The thermoset bonding/formingprocess is often referred to as curing. Different combination ofcomponents or precursors, as well as different chemical reactions can beused for forming the desired thermoset.

Therefore, the present invention includes both conductive thermosets aswell as conductive thermoset precursors or components used to makeconductive thermosets. Methods for preparing conductive thermosets andconductive thermoset precursors are also disclosed herein.

It has been discovered that conductive thermosets can be formed fromconductive thermoset precursors which have been prepared from anextrusion process typically reserved for thermoplastics. Otherconventional mixing equipments or processes, such as with a Brabendermixer, planetary mixer, Waring blender, sonication, etc. may be used todisperse or mix other materials such as diluting agents into theconductive thermoset precursor.

In a preferred embodiment, a first thermoset precursor is mixed withcarbon nanotubes or carbon nanotube aggregates by extrusion (e.g., usingan extruder) to form a conductive thermoset precursor. The firstthermoset precursor may be liquid or solid. The extruder may be a singlescrew, reciprocating single screw (e.g., Buss kneader), twin screw orany other conventional extruders useful for dispersing additives in thethermoset precursor. Furthermore, the twin screw extruder may be counterrotating or co-rotating.

Extrusion of the first thermoset precursor is only feasible within acritical range of viscosities. Viscosity is often a function of shearforce and includes complex viscosity and the stress strain curve.Viscosity is explained in more detail in Macosko, Christopher W.,Rheology: Principles measurements and applications, Wiley-VCH (1994),hereby incorporated by reference. On the one hand, it has beendiscovered that the extrusion process does not generate enough shearforce to disperse carbon nanotubes or carbon nanotube aggregates inthermoset precursors with low viscosity. Conversely, thermosetprecursors with high viscosity cannot be processed through the extruder.Therefore, in one embodiment, the thermoset precursor have viscositiesgreater than 15 poise, preferably between 20 and 600 poise, morepreferably between 50 and 500 poise. Temperature may be adjusted in theextruder if necessary to obtain the desired viscosity. For example, asolid thermoset precursor is typically melted in the extruder beforeproceeding with the extrusion process. In such case, the thermosetprecursor is said to have a viscosity or melt viscosity greater than 15poise, preferably between 20 and 600 poise, more preferably between 50and 500 poise.

The state or viscosity of a conductive thermoset precursor may beadjusted by the inclusion or addition of a diluting or let down agent toobtain a more suitable viscosity or state for the extrusion process. Forexample, a conductive thermoset precursor in solid or powdered form mayinclude or may be mixed with a liquid, non-solid or gel-like dilutingagent which will result in the conductive thermoset precursor beingmaintained in a viscous liquid, non-solid or gel-like state. Thediluting agent includes thermoset precursor which upon addition does notreact with the first thermoset precursor to cure or become the finalthermoset product. The diluting or let down agent may be included, mixedor added by use of a planetary mixer, Brabender mixer, Waring blender,sonicator or other conventional mixing equipment which generates therequisite level of shear or force to facilitate mixing of suchingredients.

To form commercially viable conductive thermosets, it is preferred thatthe conductive thermoset precursor contain carbon nanotube or carbonnanotube aggregates at loadings between 0.5 and 40%, preferably between0.5 and 30%. Other exemplary carbon nanotube or carbon nanotubeaggregate loading ranges include 5 to 40%, 1 to 15% or 5 to 15%.

Once a conductive thermoset precursor has been formed, a conductivethermoset can then be made by reacting the conductive thermosetprecursor with the corresponding known second thermoset precursor toform the conductive thermoset, which will preferably have a 1 to 5%carbon nanotube or carbon nanotube aggregate loading. The secondthermoset precursor may or may not contain carbon nanotube or carbonnanotube aggregates. The conductive thermoset may have a resistivityless than 10¹¹ ohm-cm, preferably less than 10⁸ ohm-cm, more preferablyless than 10⁶ ohm-cm.

It has been further discovered that where the first thermoset precursorcontain epoxide (a reactive three member oxygen group), the amount ofepoxides in the precursor can affect the dispersion of the carbonnanotubes and carbon nanotube aggregates therein. In one embodiment, theweight per epoxide of the first thermoset precursor is greater than 600gram precursor/gram equivalent epoxide. Preferably, the weight perepoxide in the first thermoset precursor is between 600 and 4000 gramprecursor/gram equivalent epoxide. More preferably, the weight perepoxide in the first thermoset precursor is between 1000 and 3800 gramprecursor/gram equivalent epoxide.

Since the first thermoset precursor may need to be melted in order to beused with the extrusion process, the melting point of the firstthermoset precursor may also play a role in affecting the dispersion ofthe carbon nanotubes and carbon nanotube aggregates. It is preferredthat the melting point of the first thermoset precursor be greater than30° C., or conveniently between 30 and 350° C. Higher melting pointdecreases the likelihood of feedstock bridging in the feed port of theextruder. However, one skilled in the art will understand that theextruder can be cooled as necessary to temperatures as low as −40° C. byusing an appropriate coolant in order to obtain viscosity within thepreferred range.

The following sections describe various methods of preparing specificconductive thermoset precursors and conductive thermosets with epoxy,polyester, vinyl ester and silicone. All of the discussions under thissection apply to these subsequent sections (i.e., procedure, epoxide,viscosity, carbon nanotube or carbon nanotube aggregate disclosure,melting point, resistivity, etc.). Further, one skilled in the art willrecognize that these descriptions are not exhaustive and can be modifiedin accordance with the teachings herein. Moreover, these specificconductive thermoset description, coupled with the general conductivethermoset description, provide one skilled in the art with the knowledgeand skill to prepare any other conductive thermoset precursors orconductive thermosets such as conductive urethane and phenolics.

Methods of Preparing Conductive Epoxy Precursors and Conductive EpoxyResins

Epoxy is a well known thermoset having a variety of uses andapplications such as surface coatings, adhesives, castings, panels,shielding materials, etc. Conductive epoxy resins would find use in anumber of applications, including in high temperature applications(e.g., up to 160° C.). Conductive epoxy resins would be useful tofacilitate electrostatic dissipation (e.g., ESD pre-preg for aviationindustry, ESD adhesives for electronics assembly, etc.) Conductive epoxyresins can be used as coatings for galvanic corrosion protection.Conductive epoxy resins would also be useful in making low cost tool bypermitting chrome plating on the epoxy mold surface.

Epoxy resins typically contain epoxide groups, which are reactive threemember oxygen groups. Epoxy resins are formed from a number ofconventional and known epoxy precursors. One common combination isepichlorohydrin and the aromatic bisphenol A. Alternatively, epoxy canbe formed from epichlorohydrin and aliphatic polyols such as glycerol.Epoxy may also be made by starting with di-epoxide compounds and curingthem with diamines. Another method for forming epoxy resins includeoxidizing polyolefins with peracetic acid and curing with anhydrides athigh temperatures.

Epoxy resins can be cured by heat or by passing a current though theepoxy, thereby reducing heating costs and improving quality control inthe manufacture of parts and assemblies. The ability to cure with anelectrical current make epoxy a very useful adhesive in military andaerospace applications.

In a preferred embodiment, conductive epoxy precursors are prepared bymixing a first epoxy precursor with carbon nanotubes or carbon nanotubesaggregates via extrusion. The conductive epoxy precursor may furtherinclude a diluting or let down agent (or may be mixed with such) toadjust the viscosity or state of the conductive epoxy precursor. Thediluting or let down agent may be included, mixed or added by use of aplanetary mixer, Brabender mixer or other conventional mixing equipmentwhich generates the requisite level of shear or force to facilitatemixing of such ingredients. The diluting or let down agent can be otherepoxy precursors which, when included, mixed or added to the conductiveepoxy precursor, will not upon addition to the conductive epoxyprecursor cure to form the final epoxy resin.

To form the desired conductive epoxy resin, the conductive epoxyprecursor is then mixed or reacted with another epoxy precursor (and/orother components as necessary).

It is preferred that the carbon nanotube or carbon nanotube aggregateloading in the conductive epoxy precursor be between 0.5 and 40%,preferably between 0.5 and 30%. Other exemplary carbon nanotube orcarbon nanotube aggregate loading ranges in the conductive epoxyprecursor include 5 to 40%, 1 to 15% or 5 to 15%. The second epoxyprecursor may or may not contain carbon nanotubes or carbon nanotubeaggregates. The mixture is then cured, and the final conductive epoxyproduct can contain between 1 to 5% carbon nanotube or carbon nanotubeaggregate loading. One skilled in the art will recognize that theconductive loading of the final product is flexible and is controlled bythe respective conductive loading in the first and second epoxyprecursors.

It has been discovered that the amount of epoxides in the epoxyprecursor can affect the dispersion of the carbon nanotubes and carbonnanotube aggregates therein. In one embodiment, the weight per epoxideof the first epoxy precursor is greater than 600 gram precursor/gramequivalent epoxide. Preferably, the weight per epoxide in the firstepoxy precursor is between 600 and 4000 gram precursor/gram equivalentepoxide. More preferably, the weight per epoxide in the first epoxyprecursor is between 1000 and 3800 gram precursor/gram equivalentepoxide.

It has also been discovered that the viscosity of the first epoxyprecursor also affects the dispersion of the carbon nanotubes and carbonnanotube aggregates therein. In one embodiment, the first epoxyprecursor has a viscosity greater than 15 poise. Preferably, the firstepoxy precursor has a viscosity between 20 to 600 poise, more preferablybetween 50 and 500 poise.

The melting point of the first epoxy precursor may also play a role inaffecting the dispersion of the carbon nanotubes and carbon nanotubeaggregates. It is preferred that the melting point of the first epoxyprecursor be greater than 30° C., more preferably between 30 and 350° C.Higher melting point decreases the likelihood of feedstock bridging inthe feed port of the extruder.

Methods of Preparing Other Conductive Thermoset Precursors andConductive Thermosets Polyester

Polyester is another popular thermoset having a number of uses inreinforcing plastics, automotive parts, boat hulls, foams, protectivecoatings, structural applications, pipings, etc. As such, conductivepolyester would also find a number of useful applications as well.

Precursor polyester resins are made by reacting dicarboxylic acids (forexample, maleic and phthalic acids) with glycols (for example, propyleneand diethylene glycols) in a jacketed and agitated reactor kettle. Inpractice, the anhydrous forms of the dicarboxylic acids are preferred.The process is a batch operation, with cycle “cook” times ranging from 6up to 24 hours, depending on the type of precursor resin being made.

As the reaction proceeds in the kettle, the polymer molecular weightincreases, causing the viscosity to increase and the acid value todecrease. These two precursor resin properties are continually monitoredto determine when the resin has met the predetermined end point. Whenthe end point is met, the reaction is stopped and the hot precursorresin mixture is transferred into an agitated “drop” tank containingstyrene monomer. The styrene monomer acts as both a solvent for themolten resin and also as a cross-linking agent when used by thefabricator or end-user. By this stage, the resin precursor would havecooled down (e.g. to around 80° C.).

At any stage in the preparation of the polyester precursor resin, carbonnanotubes or carbon nanotube aggregates can be mixed with the polyesterprecursor resin and extruded in accordance with a preferred embodimentto form the conductive polyester precursor. The carbon nanotube orcarbon nanotube aggregates may be added at a 0.5 and 40% loading,preferably between 0.5 and 30%. Other exemplary carbon nanotube orcarbon nanotube aggregate loading ranges include 5 to 40%, 1 to 15% or 5to 15%.

Once extruded, the conductive polyester precursor resin can be furthermodified using conventional techniques to meet various predeterminedrequirements such as resin viscosity and reactivity properties.

To form conductive polyester, the conductive polyester precursor resins,which have reactive sites resulting from the incorporation of theanhydrous forms of unsaturated diacarboxylic acids (e.g. maleicanhydride), are crosslinked with the styrene monomer via a free radicalreaction. Liquid styrene or other reactive unsaturated monomers may beused to crosslink the conductive polyester precursor resin. Thisreaction can be initiated by the addition of a catalyst, such as aperoxide catalyst (e.g., methyl ethyl ketone peroxide (MEKP)). The finalconductive polyester product can contain between 1 to 5% carbon nanotubeor carbon nanotube aggregate loading

Vinyl Ester

Another thermoset having a variety of useful application is vinyl ester.Unlike polyester, vinyl ester do not absorb as much water, and do notshrink as much when cured. Vinyl esters also have very good chemicalresistance and bond well to glass due to the presence of hydroxylgroups. As such, conductive vinyl ester precursors and conductive vinylesters would also find a number of practical uses.

Vinyl ester resin precursors are made by reacting a di-epoxide withacrylic acid, or methacrylic acid:

Larger oligomers such as the following can be used as well:

Carbon nanotubes or carbon nanotube aggregates can be mixed with thedi-epoxide component of the vinyl ester precursor before or after themixing with acrylic acid, and the mixed precursor resin extruded inaccordance with a preferred embodiment to form a conductive vinyl esterprecursor resin. The carbon nanotube or carbon nanotube aggregates maybe added at a 0.5 and 40% loading, preferably between 0.5 and 30%. Otherexemplary carbon nanotube or carbon nanotube aggregate loading rangesinclude 5 to 40%, 1 to 15% or 5 to 15%.

In a preferred embodiment, the polyester or vinyl ester precursor is abisphenol A derivative. As such, a preferred conductive precursorcomprises a bisphenol A derivative and carbon nanotubes or carbonnanotube aggregates. The preferred conductive precursor is formed byextruding the bisphenol A derivative and carbon nanotubes or carbonnanotube aggregates under conditions sufficient to disperse the nanotubeor aggregates in the bisphenol A derivative.

The conductive vinyl ester precursor resin is then cured or crosslinkedto form vinyl ester by polymerizing the vinyl groups. The finalconductive vinyl ester product can contain between 1 to 5% carbonnanotube or carbon nanotube aggregate loading.

Silicone

Yet another thermoset which has a number of useful applications issilicone. Silicone precursors come in a variety of differentviscosities. It has been discovered that certain silicone precursors arehave viscosities at room temperature which are conducive to theextrusion process. These silicone precursors are thus unique over anumber of thermoset precursors in that they do not need to be meltedfirst at an elevated temperature in order to be used with the extrusionprocess.

Thus, a conductive silicone precursor can be formed by extruding carbonnanotubes or carbon nanotube aggregates with a first silicone precursorin accordance with a preferred embodiment. Preferably, the siliconeprecursor has a viscosity at room temperature which is amenable to theextrusion process. An example of such silicone precursor isvinylterminated polydimethylsiloxane. The carbon nanotube or carbonnanotube aggregates may be added at a 0.5 and 40% loading, preferablybetween 0.5 and 30%. Other exemplary carbon nanotube or carbon nanotubeaggregate loading ranges include 5 to 40%, 1 to 15% or 5 to 15%.

The conductive silicone precursor can then be mixed with a secondsilicone precursor (or reacted with air or other elements if no secondsilicone precursor is needed) to form the conductive silicone. The finalconductive silicone product can contain between 1 to 5% carbon nanotubeor carbon nanotube aggregate loading

EXAMPLES

The following examples serve to provide further appreciation of theinvention but are not meant in any way to restrict the effective scopeof the invention.

Example 1

Experiments were conducted with EPON 1001F, an epoxy precursor made andsold by Resolution Performance Products with a weight per epoxide of525-550 gram precursor/gram equivalent epoxide (as measured by HC-427Gor ASTM D-1652-97 perchloric acid methods), melt viscosity of 4.4 poise(as measured by HC-710B or ASTM D-2196-86 (1991) el at 150° C. byBrookfield Viscometer), and melting point range of 70 to 80° C.

5 weight-% of BN carbon nanotube aggregates were added to EPON 1001F andsent through a co-rotating twin screw extruder having the followingsettings:

Parameter Set Point Actual Feed Zone, ° F. 100 100 Zone 1, ° F. 150 149Zone 2, ° F. 200 200 Zone 3, ° F. 200 200 Zone 4, ° F. 185 185 Zone 5, °F. 160 160 Zone 6, ° F. 160 160 Zone 7, ° F. 160 160 Zone 8, ° F. 170170 Zone 9, ° F. 180 181 Die Zone 1, ° F. 200 204 Screw Speed, RPM — 150% Load — 43 Side Stuffer, RPM — 125 Polymer Feeder, Dial — 301 FibrilFeeder, Dial — 167 Melt Temperature, ° F. — 218 Head Pressure, psi — 12Rate, lbs/hr — 8.0

Experiments with EPON 1001F were not successful as the material couldnot be processed due to the low viscosity. The material also bridged inthe feed throat. A number of processing parameters were adjusted but didnot result in an acceptable extrusion. Thus, this experiment wasaborted.

Example 2

Experiments were conducted with EPON 1009F, an epoxy precursor made andsold by Resolution Performance Products with a weight per epoxide of2300-3800 gram precursor/gram equivalent epoxide (as measured by HC-427Gor ASTM D-1652-97 perchloric acid methods), melt viscosity greater than500 poise (as measured by HC-710B or ASTM D-2196-86 (1991) el at 150° C.by Brookfield Viscometer), and melting point range of 130 to 140° C.

15 weight-% of BN carbon nanotube aggregates were added to EPON 1009Fand sent through a co-rotating twin screw extruder having the followingsettings:

Parameter Set Point Actual Feed Zone, ° F. 90 91 Zone 1, ° F. 210 210Zone 2, ° F. 290 290 Zone 3, ° F. 290 290 Zone 4, ° F. 255 256 Zone 5, °F. 255 255 Zone 6, ° F. 255 255 Zone 7, ° F. 255 255 Zone 8, ° F. 255255 Zone 9, ° F. 290 290 Die Zone 1, ° F. 290 290 Screw Speed, RPM — 150% Load — 88 Side Stuffer, RPM — 125 Polymer Feeder, Dial — 156 FibrilFeeder, Dial — 247 Melt Temperature, ° F. — 344 Head Pressure, psi — naRate, lbs/hr — 4.0

The strand was successfully extruded onto a conveyor belt, allowing forair cooling before being fed into a pelletizer. The material was easilypelletized with little evidence of brittleness caused by polymerdegradation. At these conditions the product ran at steady state forover 2 hours before the run was terminated.

Example 3

BN carbon nanotube aggregates are added to the following epoxyprecursors sold by Resolution Performance Products using a twin screwextruder:

Fusion Solids:

MELT MELTING WEIGHT PER VISCOSITY² POINT GRADE EPOXIDE¹ Poise ° C. 1002F600-700 12-25 80-90 1004F 800-950 18  90-100 1007F 1700-2300 App. 500120-130 ¹Test Method HC-427G or ASTM D-1652-97 (Perchloric Acid Method);grams or resin (solids basis) containing one gram-equivalent of epoxide.Perchloric acid titration methods vary depending upon resin. ²TestMethod HC-710B or ASTM D-2196-86(1991)e1 at 150° C. (Viscosity byBrookfield Viscometer.

Powder Coating/Molding Powder Solids:

MELT MELTING WEIGHT PER VISCOSITY² POINT GRADE EPOXIDE¹ Poise ° C. 2002675-760 20-40 80-90 2003 725-825 30-50 90-95 2004 875-975  70-120 95-105 2005 1200-1400 >300 110-120 2012 510-570 20-35 80-90 2014750-850 200-600 100-120 2024 850-950  60-120  95-105 2042 700-750  8-1675-85 ¹Test Method HC-427G or ASTM D-1652-97 (Perchloric Acid Method);grams or resin (solids basis) containing one gram-equivalent of epoxide.Perchloric acid titration methods vary depending upon resin. ²TestMethod HC-710B or ASTM D-2196-86(1991)e1 at 150° C. (Viscosity byBrookfield Viscometer.

Example 4

33 grams of 30% BN/Epon 1009F concentrate is prepared and combined with24 grams of ethyl 3-ethoxy propionate (“e3ep”) and 24 grams of xyleneusing a low shear mixer. This first mixture is aged for two days.

23 grams of virgin Epon 1009F is combined with 17 grams of e3ep, 17grams of xylene, 29 grams of methylon 75202, 1.3 grams of SR 882M, 1.4grams of 85% phosphoric acid and 10 grams of n-butanol to form a secondmixture.

The two mixtures are combined to make a coating solution containingapproximately 2.3% nanotubes by weight.

Example 5

The combined mixture in Example 4 above is diluted with more e3ep untilthe viscosity is 20 seconds as measured by a No. 4 Ford Cup to produce aproduct suitable for spray coating.

Example 6

33 grams of 30% BN/Epon 1009F concentrate is prepared and combined with24 grams of ethyl 3-ethoxy propionate (“e3ep”) and 24 grams of xyleneusing a low shear mixer to form a first mixture.

77 grams of TiO₂ and 23 grams of virgin Epon 1009F is combined with 17grams of e3ep, 17 grams of xylene, 29 grams of methylon 75202, 1.3 gramsof SR 882M, 1.4 grams of 85% phosphoric acid and 10 grams of n-butanolto form a second mixture.

Both mixtures are aged for two days and then are combined to make acoating solution.

Example 7

Conductive thermosets containing carbon nanotubes can be used to formconductive bi-polar plate for use with fuel cells. For example, adesired conductive thermoset can comprise carbon nanotubes and athermoset phenol formaldehyde or phenolic resin.

Cotton candy (“CC”) fibril aggregates from Hyperion were mixed with athermoset phenolic precursor (resin without the cross-linkingadditives). The resin precursor was in a powdered form that crystallizedafter sitting on the shelf. The resin precursor was run through a hammermill in order to pulverize it back into a powder. Compounding trialswere then run on the 27 mm Leistritz in both counter and co-rotatingmodes.

The first attempt at compounding this material was in counter rotatingmode. The processing profile was as follows:

RUN NUMBER (S) 10184 MODE Counter-rotating PARAMETER SET POINT ACTUALFeed Zone, ° F. 130 128 Zone 1, ° F. 170 170 Zone 2, ° F. 245 245 Zone3, ° F. 245 245 Zone 4, ° F. 230 231 Zone 5, ° F. 230 231 Zone 6, ° F.230 230 Zone 7, ° F. 215 215 Zone 8, ° F. 215 215 Zone 9, ° F. 210 210Die Zone 1, ° F. 215 215 Screw Speed, RPM — 150 % Load — 71 SideStuffer, RPM — 125 Polymer Feeder, Dial — 83 Fibril Feeder, Dial — 187Melt Temperature, ° F. — 290 Head Pressure, psi — 150 Rate, lbs/hr — 5.0

The initial fibril concentration was 10%. The load on the motor was highat this loading, so the concentration was lowered to 5%. For reasonsunknown, this experiment was not successful. Varying temperatures, screwspeeds, and feed rates did not alleviate the problem. When the screwswere pulled, uncompounded dry carbon was “caked” in the first mixingsection after the carbon feed port. This may have been due to theimproper screw design. In the counter rotation mode, no material sampleswere collected.

The mixing of carbon nanotubes in the thermoset precursor was thenattempted in co-rotating mode. Carbon concentrations of 7 and 10 wt %were compounded with some success. The processing parameters were asfollows:

RUN NUMBER (S) 10185 MODE Co-rotating PARAMETER SET POINT ACTUAL FeedZone, ° F. 135 132 Zone 1, ° F. 150 150 Zone 2, ° F. 250 249 Zone 3, °F. 250 250 Zone 4, ° F. 230 230 Zone 5, ° F. 230 230 Zone 6, ° F. 220220 Zone 7, ° F. 210 210 Zone 8, ° F. 210 210 Zone 9, ° F. 220 220 DieZone 1, ° F. 240 238 Screw Speed, RPM — 175 % Load — 85 Side Stuffer,RPM — 125 Polymer Feeder, Dial — 97-96 Fibril Feeder, Dial — 116-157Melt Temperature, ° F. — 75-86 Head Pressure, psi — 150-200 Rate, lbs/hr— 3.0

It was seen that even at these relatively low loadings and lowthroughputs, the load on the motor was high (between 75 and 86%). Thisresult was somewhat surprising as the phenolic resin precursor has avery low viscosity in the molten state. In addition, the materialre-crystallized in the feed throat leading to an overload on the motorat one point.

A different grade of phenolic precursor such as one with a lowermolecular weight and a narrower molecular weight distribution (i.e.,lower concentration of the lower molecular weight fraction) may lead tobetter results on the theory that the low molecular weight tails aresomehow reacting negatively with the carbon nanotubes duringcompounding.

Example 8

Conductive phenolic resin precursors were made with carbon nanotubes anda phenolic base resin precursor with a lower molecular weight but anarrower molecular weight distribution. It has been theorized thathigher MW material (broader MW distribution) had a significant fractionof fringe material that was reacting negatively with the carbon.Therefore, by minimizing the fringe material, it was expected that theprocessability should be improved.

Phenolic base resin precursor and carbon nanotubes were compoundedsuccessfully at a concentration of 15 wt-% fibrils at the followingconditions:

RUN NUMBER (S) 10215 MODE Co-rotating PARAMETER SET POINT ACTUAL FeedZone, ° F. 75 101 Zone 1, ° F. 150 150 Zone 2, ° F. 250 250 Zone 3, ° F.250 250 Zone 4, ° F. 230 230 Zone 5, ° F. 220 221 Zone 6, ° F. 210 210Zone 7, ° F. 210 210 Zone 8, ° F. 210 210 Zone 9, ° F. 210 210 Die Zone1, ° F. 220 222 Screw Speed, RPM — 150 % Load — 89 Side Stuffer, RPM —125 Polymer Feeder, Dial — 82 Fibril Feeder, Dial — 226 MeltTemperature, ° F. — 260 Head Pressure, psi — 301 Rate, lbs/hr — 3.0

It has been discovered that phenolic resin precursors with narrower MWDresulted in better compounding of carbon nanotubes.

Example 9

A ten pound sample was made with the lower viscosity (narrow molecularweight distribution) phenolic resin precursor. The sample contained 15wt-% CC fibrils.

The masterbatch was processed at the following conditions:

RUN NUMBER (S) 10237 MODE Co-rotating PARAMETER SET POINT ACTUAL FeedZone, ° F. 75 102 Zone 1, ° F. 150 150 Zone 2, ° F. 240 240 Zone 3, ° F.240 240 Zone 4, ° F. 220 220 Zone 5, ° F. 220 220 Zone 6, ° F. 210 210Zone 7, ° F. 210 210 Zone 8, ° F. 210 212 Zone 9, ° F. 210 210 Die Zone1, ° F. 220 222 Screw Speed, RPM — 150 % Load — 80 Side Stuffer, RPM —125 Polymer Feeder, lbs/hr — 2.55 Fibril Feeder, Dial — 226 MeltTemperature, ° F. — 302 Head Pressure, psi — 150 Rate, lbs/hr — 3.0

Example 10

Carbon nanotube was combined with phenolic resin precursor of an evenlower molecular weight distribute than Example 9 on the 27 mm Leistritz.

The carbon nanotubes were fed through the side stuffer on the 27 mmLeistritz at the following conditions:

RUN NUMBER (S) 10350 MODE Co-rotating PARAMETER SET POINT ACTUAL FeedZone, ° F. 75 118 Zone 1, ° F. 150 150 Zone 2, ° F. 230 231 Zone 3, ° F.230 230 Zone 4, ° F. 190 190 Zone 5, ° F. 190 191 Zone 6, ° F. 180 180Zone 7, ° F. 180 180 Zone 8, ° F. 180 181 Zone 9, ° F. 180 179 Die Zone1, ° F. 200 201 Screw Speed, RPM — 150 % Load — 82 Side Stuffer, RPM —125 Polymer Feeder, Dial — 139 Fibril Feeder, Dial — 250 MeltTemperature, ° F. — 260 Head Pressure, psi — 260 Rate, lbs/hr — 3.0

It has been discovered that phenolic resin precursors with a very narrowmolecular weight distribution did not compound with carbon nanotube assmoothly as the phenolic resin precursor of Examples 8 and 9. The feedthroat would continually need to be cleaned out manually in order toprevent bridging. Also, from an aesthetic point of view, the extrudatewas not as good as the sample made in Examples 8 and 9. Approximately 10pounds were collected.

Example 11

The conductive phenolic resin precursors of Examples 8 and 9 are madeinto plates for use in fuel cells. Electrical resistivity (surfaceresistance in ohm/sq) below 50 ohm/sq., preferably 10-20 ohm/sq issought.

Example 12

Bird nest fibril aggregates (“BN”) was combined with phenolic resinprecursor using the procedure as described in Example 8.

The masterbatch was successfully produced at the following conditions:

RUN NUMBER (S) 10514 thru 10517 MODE Co-rotating PARAMETER SET POINTACTUAL Feed Zone, ° F. 110 113 Zone 1, ° F. 150 150 Zone 2, ° F. 240 239Zone 3, ° F. 240 240 Zone 4, ° F. 220 219 Zone 5, ° F. 220 219 Zone 6, °F. 210 210 Zone 7, ° F. 210 210 Zone 8, ° F. 210 210 Zone 9, ° F. 210210 Die Zone 1, ° F. 230 228 Screw Speed, RPM — 127 % Load — 75 SideStuffer, RPM — 125 Polymer Feeder, Dial — 079 Fibril Feeder, Dial — 187Melt Temperature, ° F. — 260 Head Pressure, psi — — Rate, lbs/hr — 3.0

Fifty (50) pounds were collected.

Example 13

Carbon nanotubes was mixed with EPON 1009, a known epoxy precursor,using an extrusion process to form a conductive epoxy precursorcontaining 15% carbon nanotubes by weight and having a melting point of140° C. The conductive epoxy precursor was ground fine enough so as topass through a #20 sieve.

A liquid or gel-like diluting agent, EPON 828, was mixed in or added tothe conductive epoxy precursor in varying amounts. The conductive epoxyprecursor was heated to 150° C., then 170° C. to facilitate the mixing.Initial attempts to mix in the EPON 828 using a planetary mixer with lowshear rate (Ross Mixers, Hauppauge, N.Y.) were not successful.Subsequent attempts to mix in the EPON 828 using a multi shaft mixerwith greater shear rate, VersaMix (VM) (Ross Mixers, Hauppauge, N.Y.)were successful. Samples 1-13 were prepared. Sample 11 was prepared byadding more EPON 828 to Sample 10, which appeared more viscous than theVersaMix could mix homogenously. Samples 1-12 were withdrawn andadditional ground conductive epoxy precursor was added during severalhours of processing at temperature. Sample 13 was made as a single,uninterrupted batch.

EPON EPON Sample 828 1009 CNT CNT Total No. (g) (g) (g) (%) (g) WPE* 15493 333 59 1.00 5885 199 2 5493 690 122 1.93 6305 210 3 5252 660 1161.93 6028 210 4 5002 628 111 1.93 5742 210 5 5002 1087 192 3.05 6282 2266 4802 1044 184 3.05 6030 226 7 4802 1514 267 4.06 6583 242 8 4573 1442254 4.05 6269 242 9 4573 2003 353 5.10 6929 263 10 4401 1927 340 5.106669 263 11 6126 1927 340 4.05 8394 242 12 5915 1861 328 4.05 8105 24213 5448 1182 209 3.05 6839 226 *WPE = Weight per Epoxy Equivalent.

The materials are all viscous, with the higher levels bordering onsolids at room temperature.

Example 14

Selected samples of conductive epoxy precursor from Example 13 wereblended with a second epoxy precursor, Epi-cure 3234 curing agent, toform the conductive epoxy and the resistivity of the cured specimenswere measured. Both the conductive epoxy precursor samples, which wereviscous, and Epi-cure 3234, which is a tri-amine liquid at roomtemperature, was heated in order to accelerate curing. EpiCure 3234 wasadded by stoichiometry based on WPE and was approximately 11% by weight.

In addition, conductive epoxy precursors in which EPON 828 was added ormixed in with either a Waring blender (WB) or with sonication (SON) arealso included. These samples are labeled H1-H7.

Most of the conductive epoxy samples were prepared by adding theconductive epoxy precursor and the Epi-cure 3234 to a zip-lock PE bag,warmed on an 80° C. hotplate, and mixed with a hand roller. The mixedsample was squeezed from the PE bag onto a PTFE sheet and covered with aweighted piece of PTFE to form a flat, cured specimen. Curing was eitherin an oven, on a hot plate or in the Carver press with heated platens.Small pieces of the cured conductive epoxy were cut, opposing surfacessanded and coated with Ag paint. Resistance was measured with a DMM(digital multimeter).

To investigate the possible effect of curing temperature, a sample ofSample 6 and Epi-cure 3234 was warmed to 60° C., mixed with the rollerand then split into 3 parts with one part cured at room temperature(6-RT), one at 80° C. on the hot plate (6-HP) and the third at 116° C.in the Carver press (6-CP). The 6-RT room temperature sample was verybrittle and its resistance was off scale on the DMM (limit 2E7 ohms). Inanother experiment, another 6-RT sample prepared from the first tworolls of a three roll mill. The resulting sample was also very brittleand its resistance off scale on the DMM. Even though Ag paint was used,contact resistance may have been an issue.

Data for the resistivity experiment is summarized below:

Let CC Down Mixing Cure Sample CNT Mixing Temp Resistance Length HeightWidth Resistivity Temp No. (%)* Method (° C.) (Ohms) (in) (in) (in)(Ohm-cm) (° C.) H1 2 WB 170 5.50E+05 0.795 0.055 0.3 2.90E+04 80 H2 2SON 150 3.00E+05 0.775 0.055 0.26 1.40E+04 80 H3 2 WB 150 7.60E+05 0.8250.036 0.29 2.40E+04 80 H4 2 SON ~100 2.50E+05 0.57 0.065 0.3 2.20E+04 80H5 1 SON ~100 1.17E+06 0.38 0.035 0.23 6.30E+04 80 H6 1.2 WB ~1001.53E+06 0.46 0.045 0.25 9.50E+04 80 H7 3 WB 160 1.20E+06 0.595 0.020.28 2.90E+04 100 3-1 2 VM 150-170 >2e7 80 3-2 2 VM 150-170 >2e7 80 4-12 VM 150-170 >2e7 80 4-2 2 VM 150-170 >2e7 80 4-Disk 2 VM 150-1701.98E+06 0.62 0.04 0.8 2.60E+05 80 4-Rect 2 VM 150-170 1.29E+06 1.530.125 0.82 2.20E+05 80 3 2 VM 150-170 1.19E+05 0.09 0.375 0.46 5.79E+05120 6-1 3 VM 150-170 2.71E+06 0.325 0.0105 0.195 4.30E+04 80 6-2 3 VM150-170 1.74E+06 0.45 0.013 0.19 2.40E+04 80 6 3 VM 150-170 4.05E+061.765 0.14 0.45 3.67E+05 120 12 4 VM 150-170 2.00E+02 0.488 0.132 0.0811.10E+01 100 12 4 VM 150-170 5.30E+05 0.38 0.0165 0.161 9.40E+03 100 7 4VM 150-170 3.30E+03 0.065 0.41 0.42 2.22E+04 120 11 4 VM 150-1704.93E+04 0.065 0.495 0.478 4.56E+05 120 6-RT 3 VM 150-170 >2e7 0.038 206-HP 3 VM 150-170 9.88E+03 0.038 0.315 0.325 6.8E+04 80 6-CP 3 VM150-170 9.70E+05 0.038 0.37 0.36 8.6E+06 116 6-RM 3 VM 150-170 >2e70.038 20 *CNT % was calculated prior to addition of the curing agent.The WPE of EPON 828 is 188 and the WPE of EPON 1009F used forcalculations was 3000.

The above example confirmed that cured epoxies with ESD levels ofconductivity can be obtained by letting down a conductive epoxyprecursor with a diluting agent to loading levels of ˜1-4%.

The terms and expressions which have been employed are used as terms ofdescription and not of limitations, and there is no intention in the useof such terms or expressions of excluding any equivalents of thefeatures shown and described as portions thereof, it being recognizedthat various modifications are possible within the scope of theinvention.

1. A method of preparing a conductive thermoset precursor comprising:providing a first thermoset precursor having a viscosity greater than 15poise, and dispersing carbon nanotubes in said first thermoset precursorby extrusion to form a conductive thermoset precursor, wherein saidcarbon nanotubes have a diameter less than 1 micron.
 2. The method ofpreparing the conductive thermoset precursor of claim 1, wherein saidfirst thermoset precursor is an epoxy precursor, phenolic precursor,polyimide precursor, urethane precursor, polyester precursor, vinylester precursor or silicone precursor.
 3. The method of preparing theconductive thermoset precursor of claim 1, wherein said first thermosetprecursor is a bisphenol A derivative.
 4. The method of preparing theconductive thermoset precursor of claim 1, wherein the weight perepoxide in said first thermoset precursor is in the range of 600 to 4000gram precursor/gram equivalent epoxide.
 5. The method of preparing theconductive thermoset precursor of claim 1, wherein the viscosity of saidfirst thermoset precursor is in the range of 20 to 600 poise.
 6. Themethod of preparing the conductive thermoset precursor of claim 1,wherein the melting point of said first thermoset precursor is between30 and 350° C.
 7. The method of preparing the conductive thermosetprecursor of claim 1, wherein said carbon nanotubes include singlewalled carbon nanotubes having diameters less than 5 nanometers.
 8. Amethod of preparing a conductive thermoset precursor comprising:providing a first thermoset precursor having a viscosity greater than 15poise, and dispersing carbon nanotubes in said first thermoset precursorby extrusion to form a conductive thermoset precursor, wherein saidcarbon nanotubes have a diameter less than 1 micron: wherein said carbonnanotubes are in the form of aggregates of carbon nanotubes, saidaggregates having a macromorphology resembling birds nest, cotton candy,combed yarn or open net.
 9. The method of preparing the conductivethermoset precursor of claim 1, wherein said extrusion process includesthe use of a co-rotating or counter rotating twin screw extruder. 10.The method of preparing the conductive thermoset precursor of claim 1,wherein the concentration of said carbon nanotube is in the range of 0.5to 30% by weight.
 11. The method of preparing the conductive thermosetprecursor of claim 1, further comprising adding a diluting agent to theconductive thermoset precursor.
 12. The method of preparing theconductive thermoset precursor of claim 11, wherein the diluting agentis a second thermoset precursor which does not react, upon addition tothe conductive thermoset precursor, with said first thermoset precursorto cure into a final thermoset product.
 13. A method of preparing aconductive thermoset containing carbon nanotubes comprising: preparing aconductive thermoset precursor by a method comprising: providing a firstthermoset precursor having a viscosity greater than 15 poise, anddispersing carbon nanotubes in said first thermoset precursor byextrusion to form a conductive thermoset precursor, wherein said carbonnanotubes have a diameter less than 1 micron; and reacting saidconductive thermoset precursor with at least a second thermosetprecursor to form a conductive thermoset, wherein: said first thermosetprecursor has a viscosity greater than 15 poise, said second thermosetprecursor has a viscosity less than said first thermoset precursor, andsaid carbon nanotubes have a diameter less than 1 micron.
 14. The methodof claim 13, wherein preparing the conductive thermoset precursorfurther comprises adding a diluting agent to the conductive thermosetprecursor.
 15. A conductive thermoset precursor formed by the method ofclaim
 1. 16. A conductive thermoset precursor formed by the method ofclaim
 11. 17. A conductive thermoset formed by the method of claim 13wherein said carbon nanotubes are in the form of aggregates of carbonnanotubes, said aggregates having a macromorphology resembling birdsnest, cotton candy, combed yarn or open net.
 18. A conductive thermosetformed by the method of claim 14 wherein said carbon nanotubes are inthe form of aggregates of carbon nanotubes, said aggregates having amacromorphology resembling birds nest, cotton candy, combed yarn or opennet.
 19. The conductive thermoset of claim 17 wherein said thermoset isan epoxy, polyimide, phenolic, urethane, polyester, vinyl ester orsilicone polymer.
 20. The conductive thermoset of claim 17, wherein saidcarbon nanotubes include single walled carbon nanotubes having diametersless than 5 nanometers.